JP2009091457A - New polyimide foam and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyimide resin foam having a high expansion ratio and a method for producing such a polyimide foam. <P>SOLUTION: The polyimide foam consists essentially of pyromellitic acid, a diaminodiphenyl ether and a siloxane diamine. By using the method for producing such a polyimide foam by drying a polyamic acid solution which is a precursor thereof under reduced pressure to form a polyimide foam, the objective low density polyimide foam having heat resistance can be obtained. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a polyimide foam and a method for producing the same.

  The polyimide foam is used for various extreme uses as a foam resin having heat resistance derived from a polyimide resin. For example, it is widely used as a thermal insulation material for aircraft applications that require heat resistance, a thermal insulation application inside a nuclear reactor, and an aerospace application. Furthermore, in order to make the inside of an aircraft structural material light and strong, it is used in a usage method such as embedding foam.

  As a method of manufacturing such a polyimide foam, after preparing fine particles of a polyimide precursor mixed with esterified tetracarboxylic acid and diamine to form a powder, it is rapidly heated and expanded by microwave irradiation or the like. A method for producing a polyimide foam is known (for example, see Patent Document 1).

In addition, an apparatus has been proposed in which a foam is continuously produced by cooling the foam with a desired liquid after the raw resin is continuously conveyed into the decompression device to foam the raw resin (for example, , See Patent Document 2). In this method, it is said that foaming of an imide resin is also possible.
Japanese Patent No. 3687496 Japanese Patent Laid-Open No. 9-131741

  However, in the method described in Patent Document 1, it is necessary that the fine particles of the polyimide foam precursor have excellent elongation viscosity at the foaming temperature, and further there are limitations such as simultaneous occurrence of imidization reaction at a low temperature, It was necessary to produce a polyimide foam by combining specific raw materials. For example, in Patent Document 1, 50 mol% or more of the aromatic carboxylic acid component is a 2,3,3 ′, 4′-biphenyltetracarboxylic acid component, and the diamine component is 0.1 to 10 mol% of a diaminosiloxane component. Containing polyimide resin. Moreover, in the conventional method for producing a polyimide foam, in order to increase the expansion ratio of the polyimide foam, a method such as increasing the amount of a solvent as a foaming agent contained in the particles is used. The particulate polyimide precursor has problems such as difficulty in controlling foaming.

  Further, in the method of Patent Document 2, a substantially molten thermoplastic resin or thermosetting resin can only be used, and the glass transition temperature is very high like polyimide resin, and the liquid is cooled immediately after foaming. In this method, even when a foam of a polyamic acid solution is produced as in the present invention, it is difficult to produce a stable polyimide foam due to a decrease in the molecular weight of the resin. Further, when a thermoplastic polyimide resin is used, there is a need to suppress the melting temperature, and there is a problem that only a foam having low heat resistance can be manufactured.

  As a result of intensive studies to solve the above problems, the present inventors have studied a method for producing a polyimide foam composed of pyromellitic acid and diaminodiphenyl ether having excellent heat resistance and low density. In combination, it was found that a polyimide foam can be produced by adjusting the polyamic acid solution and drying the polyamic acid solution under reduced pressure, and the present invention has been completed.

That is, the present invention relates to a polyimide foam comprising at least pyromellitic acid, diaminodiphenyl ether and siloxane diamine. It is preferred foam density of the polyimide foam is ^{1kg / m 3 ~10kg / m 3} . Moreover, it is preferable that the content rate of the siloxane diamine contained in this polyimide foam is contained in the ratio of 0.5-30 mol with respect to 100 mol of all the diamines. The present invention also relates to a method for producing a polyimide foam, characterized in that a polyimide foam is formed by decompressing and drying a polyamic acid solution comprising at least pyromellitic acid, diaminodiphenyl ether and siloxane diamine.

  According to the present invention, a polyimide foam having a high expansion ratio can be easily produced, and the polyimide foam is excellent in heat resistance, mechanical properties, and chemical resistance. The polyimide foam of the present invention has a large expansion ratio, for example, use as a substitute for a flame-retardant / insulating cotton material for lightweight heat-resistant clothing, heat insulation / sound insulation material at high temperatures for automobile use, aircraft use, space It can also be used as a heat insulating material for use, and as a heat insulating sound insulating material for walls as a building member.

  Hereinafter, the present invention will be described in detail. The polyimide foam in the present invention is a foam-like molded body having a structure in which cells made of polyimide resin overlap. The polyimide foam of the present invention is a polyimide foam comprising pyromellitic acid, diaminodiphenyl ether and siloxane diamine. When it is formed into a polyimide resin by using pyromellitic acid, the elastic modulus of the polyimide foam is improved, so that a polyimide foam having excellent rigidity can be obtained, which is preferable. Further, the use of diaminodiphenyl ether is preferable because the heat resistance of the polyimide foam can be improved and the imidization reaction easily proceeds from the polyamic acid to the polyimide resin. In addition, when foam is generated in the polyamic acid solution by using siloxane diamine together, it has a foam stabilizing effect that stabilizes the foam and stabilizes the shape of the foam, making it easy to produce a polyimide foam with a high expansion ratio. This is preferable.

  Diaminodiphenyl ethers preferably used in the present invention include 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, and the like. In particular, it is preferable to use 4,4'-diaminodiphenyl ether because the heat resistance temperature of the final polyimide foam can be increased.

  Moreover, the siloxane diamine used suitably by this invention is a diamine compound which has a structure shown by General formula (1).

（式中、Ｒ_１、Ｒ_２は炭素数１〜１２のアルキル基もしくは芳香族基であり、Ｒ_１、Ｒ_２は同一であっても異なっていても良い。ｍは１〜４０の整数、ｎは１〜２０の整数を示す。）。

(In the formula, R ₁ and R ₂ are an alkyl group having 1 to 12 carbon atoms or an aromatic group, and R ₁ and R ₂ may be the same or different. M is an integer of 1 to 40, n represents an integer of 1 to 20.)

As the siloxane diamine used in the present invention, it is particularly preferable that R ₁ and R ₂ in the formula are methyl groups, m is 7 to 10, and n is 2 to 5. Use of this raw material is preferable because foaming of the polyimide resin can be easily controlled and the heat resistance of the polyimide resin is not impaired. Moreover, it is preferable that the content rate of the siloxane diamine contained in a polyimide foam is contained in the ratio of 0.5-30 mol with respect to 100 mol of all the diamines. Controlling within this range is preferable because it is easy to control foaming and has heat resistance of 400 ° C. or higher.

  Moreover, in the polyimide foam of this invention and its manufacturing method, in the range which does not impair the heat resistance and chemical resistance of a polyimide resin, acid dianhydride and diamino compound other than the above should be used as a raw material of a polyimide resin. Can do.

  For example, as the acid dianhydride, 3,3 ′, 4,4′-benzophenonic acid dianhydride, 3,3 ′, 4,4′-biphenyl acid dianhydride, 2,3,3 ′, 4- Biphenyl dianhydride can be used in combination.

  Examples of the diamino compound include m-phenylenediamine, p-phenylenediamine, bis (3-aminophenyl) sulfide, (3-aminophenyl) (4-aminophenyl) sulfide, bis (4-aminophenyl) sulfide, bis (3-aminophenyl) sulfoxide, (3-aminophenyl) (4-aminophenyl) sulfoxide, bis (4-aminophenyl) sulfoxide, bis [4- (3-aminophenoxy) phenyl] sulfoxide, bis [4- ( Aminophenoxy) phenyl] sulfoxide, (4-aminophenoxyphenyl) (3-aminophenoxyphenyl) phenyl] sulfoxide, bis [4- (4-aminophenoxy) phenyl] sulfone, (4-aminophenoxyphenyl) (3-amino Phenoxyphenyl Phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] sulfide, bis [4- (aminophenoxy) phenyl] sulfide, (4-aminophenoxyphenyl) (3-aminophenoxyphenyl) phenyl] sulfide, 3, 3′-diaminobenzanilide, 3,4′-diaminobenzanilide, 4,4′-diaminobenzanilide, bis [4- (3-aminophenoxy) phenyl] methane, bis [4- (4-aminophenoxy) phenyl ] Methane, [4- (4-aminophenoxyphenyl)] [4- (3-aminophenoxyphenyl)] methane, 1,1-bis [4- (3-aminophenoxy) phenyl] ethane, 1,1-bis [4- (4-Aminophenoxy) phenyl] ethane, 1,1- [4- (4-aminophenoxyphenyl) )] [4- (3-aminophenoxyphenyl)] ethane, 1,2-bis [4- (3-aminophenoxy) phenyl] ethane, 1,2-bis [4- (4-aminophenoxy) phenyl] ethane 1,2- [4- (4-aminophenoxyphenyl)] [4- (3-aminophenoxyphenyl)] ethane, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 2,2 -[4- (4-aminophenoxyphenyl)] [4- (3-aminophenoxyphenyl)] propane, 2,2-bis [3- (3-aminophenoxy) phenyl] -1,1,1,3 3,3-hexafluoropropane, 2,2-bis [4- (4-aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane, 2,2- [4- (4 -Aminophenoxyphenyl)] [4 (3-Aminophenoxyphenyl)]-1,1,1,3,3,3-hexafluoropropane, 1,4-bis (3-aminophenoxy) benzene, 1,4-bis (4-aminophenoxy) benzene 1,3-bis (4-aminophenoxy) benzene, 4,4′-bis (4-aminophenoxy) biphenyl, 4,4′-bis (3-aminophenoxy) biphenyl, bis [4- (3-amino Phenoxy) phenyl] ketone, bis [4- (4-aminophenoxy) phenyl] ketone, bis [4- (3-aminophenoxy) phenyl] ether, bis [4- (4-aminophenoxy) phenyl] ether, polytetra Methylene oxide-di-P-aminobenzoate, poly (tetramethylene / 3-methyltetramethylene ether) glycol bis (4- Minobenzoate), trimethylene-bis (4-aminobenzoate), p-phenylene-bis (4-aminobenzoate), m-phenylene-bis (4-aminobenzoate), bisphenol A-bis (4-aminobenzoate), 2 , 4-Diaminobenzoic acid, 2,5-diaminobenzoic acid, 3,5-diaminobenzoic acid, 3,3′-diamino-4,4′-dicarboxybiphenyl, 4,4′-diamino-3,3 ′ -Dicarboxybiphenyl, 4,4'-diamino-2,2'-dicarboxybiphenyl, [bis (4-amino-2-carboxy) phenyl] methane, [bis (4-amino-3-carboxy) phenyl] methane , [Bis (3-amino-4-carboxy) phenyl] methane, [bis (3-amino-5-carboxy) phenyl] methane, 2,2-bis [3-amino-4-carbo Cyphenyl] propane, 2,2-bis [4-amino-3-carboxyphenyl] propane, 2,2-bis [3-amino-4-carboxyphenyl] hexafluoropropane, 2,2-bis [4-amino- 3-carboxyphenyl] hexafluoropropane, 3,3′-diamino-4,4′-dicarboxydiphenyl ether, 4,4′-diamino-3,3′-dicarboxydiphenyl ether, 4,4′-diamino-2, 2'-dicarboxydiphenyl ether, 3,3'-diamino-4,4'-dicarboxydiphenyl sulfone, 4,4'-diamino-3,3'-dicarboxydiphenyl sulfone, 4,4'-diamino-2, 2'-dicarboxydiphenylsulfone, 2,3-diaminophenol, 2,4-diaminophenol, 2,5-di Minophenol, 3,5-diaminophenol, 3,3′-diamino-4,4′-dihydroxybiphenyl, 4,4′-diamino-3,3′-dihydroxybiphenyl, 4,4′-diamino-2,2 '-Dihydroxybiphenyl, 4,4'-diamino-2,2', 5,5'-tetrahydroxybiphenyl, 3,3'-diamino-4,4'-dihydroxydiphenylmethane, 4,4'-diamino-3, 3'-dihydroxydiphenylmethane, 4,4'-diamino-2,2'-dihydroxydiphenylmethane, 2,2-bis [3-amino-4-hydroxyphenyl] propane, 2,2-bis [4-amino-3- Hydroxyphenyl] propane, 2,2-bis [3-amino-4-hydroxyphenyl] hexafluoropropane, 2,2-bis [3-amino- -Hydroxyphenyl] hexafluoropropane, 3,3'-diamino-4,4'-dihydroxydiphenyl ether, 4,4'-diamino-3,3'-dihydroxydiphenyl ether, 4,4'-diamino-2,2'- Dihydroxydiphenyl ether, 3,3′-diamino-4,4′-dihydroxydiphenylsulfone, 4,4′-diamino-3,3′-dihydroxydiphenylsulfone, 4,4′-diamino-2,2′-dihydroxydiphenylsulfone 3,3′-diamino-4,4′-dihydroxydiphenyl sulfide, 4,4′-diamino-3,3′-dihydroxydiphenyl sulfide, 4,4′-diamino-2,2′-dihydroxydiphenyl sulfide, 3, , 3′-Diamino-4,4′-dihydroxydipheny Sulfoxide, 4,4′-diamino-3,3′-dihydroxydiphenyl sulfoxide, 4,4′-diamino-2,2′-dihydroxydiphenyl sulfoxide, 2,2-bis [4- (4-amino-3-hydroxy) Phenoxy) phenyl] propane, 4,4′-bis (4-amino-3-hydroxyphenoxy) biphenyl, 2,2-bis [4- (4-amino-3-hydroxyphenoxy) phenyl] sulfone, 4,4 '-Diamino-3,3'-dihydroxydiphenylmethane, 4,4'-diamino-2,2'-dihydroxydiphenylmethane, 2,2-bis [3-amino-4-carboxyphenyl] propane, 4,4' -Bis (4-amino-3-hydroxyphenoxy) biphenyl can be used in combination.

  In particular, it is preferable to use p-phenylenediamine in combination because heat resistance can be improved.

  Solvents that can be suitably used in the method for producing a polyamic acid solution of the present invention include organic polar amides such as N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, and γ-butyrolactone. Solvents, water-soluble ether compounds such as tetrahydrofuran, dioxane and dioxolane, water-soluble ketone compounds such as acetone and methyl ethyl ketone, and water-soluble nitrile compounds such as acetonitrile and propionitrile. These solvents can be used as a mixed solvent of two or more, and are not particularly limited.

  Of these, N, N-dimethylformamide, N, N-dimethylacetamide, tetrahydrofuran, dioxane, dioxolane, acetone, and methyl ethyl ketone are preferably selected from the viewpoint of the solubility and foamability of the polyamic acid.

  In the method for producing a polyamic acid solution in the present invention, the polyamic acid is preferably controlled by controlling the amount of diamine and acid dianhydride used in the organic solvent to a ratio of 0.90 to 1.10. A solution can be produced. More preferably, the reaction is carried out at 0.95 to 1.05 to form a polyamic acid. In addition, in the production of polyamic acid, it is preferable to use an acid dianhydride obtained by dehydrating an acid dianhydride because the molecular weight can be easily increased, and the purity of the acid dianhydride is that of an acid dianhydride having a ring-closed structure. It is preferable to use a material that is contained at a high purity of 98% or more. The polymer concentration of the polyamic acid solution is 0.1 to 50% by weight, particularly preferably 1 to 40% by weight, as the solid content concentration. As the polymerization conditions for the polyamic acid, the target polyamic acid can be polymerized by stirring at −20 to 50 ° C., preferably −20 to 40 ° C. in an inert gas atmosphere.

  The method for producing a polyimide foam of the present invention uses a method in which the polyamic acid solution is conveyed to an apparatus capable of reducing the pressure and dried to mold the polyimide foam. The degree of vacuum and the heating temperature of the reaction apparatus containing the polyamic acid are preferably selected as appropriate depending on the foamed state, but the degree of vacuum and the heating temperature until the polyamic acid solution evaporates are 200 Torr or less and the heating temperature is 30. It is preferable to control between 0C and 250C. If the degree of vacuum is greater than 200 Torr, the foam may break and molding may not be successful. Moreover, since the viscosity of resin will fall too much when temperature is higher than 250 degreeC, it may be unpreferable. Particularly preferred vacuum degree and heating temperature are 100 Torr or less, and foaming is preferably performed at 50 ° C. to 200 ° C. or less.

The method for controlling the expansion ratio of the foam can control the polyimide foam by adjusting the degree of vacuum and the heating temperature, and further the amount of the solvent contained. The amount of solvent is preferably adjusted as appropriate. It is preferable to adjust the amount of the solvent at a solid content concentration of the polyamic acid of 10% or more and 50% or less. Preferred because the density of the foam by adjusting this amount of the solvent, easily tune to the most preferred ^1kg / ^{m 3 ~10kg} / m 3 in the present invention. It is preferable to control a particularly preferable concentration from 15% to 30%.

Polyimide foam of the present invention, since it has become lighter material as ^{1kg / m 3 ~10kg / m 3} , use or as a substitute for light weight heat resistance clothing flame retardant, heat-insulating cotton material, LPG gas Thermal insulation for tankers, thermal insulation for extreme applications such as nuclear reactors, thermal insulation / sound insulation at high temperatures for automotive and aircraft applications, thermal insulation for space applications, and insulation insulation for walls as building materials Can also be used. Especially, it can use preferably as a sound-absorbing material and heat insulation member for the aerospace use in which weight reduction is calculated | required.

  EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples. The evaluation items in the following examples were carried out by the following methods.

[Foaming ratio]
A cube having a side of 10 cm was cut out and weighed to calculate the density.

Example 1
In a 2 L glass separable flask, a siloxane diamine (manufactured by Dow Corning Toray: trade name BY16-853U, molecular weight 910, R ₁ and R ₂ in the general formula (1) are methyl groups, n = 3 M = 9), 9.10 g (0.01 mol) and 372 g of N, N-dimethylformamide were added and stirred. To this solution, 38.1 g (0.19 mol) of 4,4-diaminodiphenyl ether was added and dissolved by stirring. Next, 43.6 g (0.20 mol) of pyromellitic dianhydride was added to obtain a polyamic acid solution (solid content concentration 18%).

上記ポリアミド酸溶液をフッ素樹脂で内壁をコーティングした円錐型の容器（直径が２０ｃｍで高さが２０ｃｍの容器）に入れて、真空乾燥装置に投入した。投入時の真空乾燥装置の温度は１００℃で投入した。また、真空度は１Ｔｏｒｒ以下になるように、一気に真空ポンプで排気した。その結果、容器内のポリアミド酸溶液は発泡して、円錐型の容器内に発泡体が得られた。
減圧状態（１Ｔｏｒｒ以下）の状態で真空オーブンを２１０℃まで昇温させて１時間真空中で焼成を行った。
内部の固形分を取り出して、１００℃から４２０℃まで１時間かけて焼成を行いポリイミド発泡体を得た。
このポリイミド発泡体の密度は５．２ｋｇ/ｍ^３であった。

The polyamic acid solution was placed in a conical container (a container having a diameter of 20 cm and a height of 20 cm) whose inner wall was coated with a fluororesin, and then placed in a vacuum drying apparatus. The temperature of the vacuum drying apparatus at the time of charging was charged at 100 ° C. The vacuum was exhausted at once with a vacuum pump so that the degree of vacuum was 1 Torr or less. As a result, the polyamic acid solution in the container foamed, and a foam was obtained in the conical container.
In a state of reduced pressure (1 Torr or less), the vacuum oven was heated to 210 ° C. and baked in vacuum for 1 hour.
The solid content inside was taken out and baked from 100 ° C. to 420 ° C. over 1 hour to obtain a polyimide foam.
The density of this polyimide foam was 5.2 kg / m ³ .

(Example 2)
In a 2 L glass separable flask, a siloxane diamine (manufactured by Dow Corning Toray: trade name BY16-853U, molecular weight 910, R ₁ and R ₂ in the general formula (1) are methyl groups, n = 3 M = 9) and 18.2 g (0.02 mol) of N, N-dimethylformamide and 363 g of N, N-dimethylformamide were added and stirred. To this solution, 36.1 g (0.18 mol) of 4,4-diaminodiphenyl ether was added and dissolved by stirring. Next, 43.6 g (0.20 mol) of pyromellitic dianhydride was added to obtain a polyamic acid solution (solid content concentration 18%).

上記ポリアミド酸溶液をフッ素樹脂で内壁をコーティングした円錐型の容器（直径が２０ｃｍで高さが２０ｃｍの容器）に入れて、真空乾燥装置に投入した。投入時の真空乾燥装置の温度は１００℃で投入した。また、真空度は１Ｔｏｒｒ以下になるように、一気に真空ポンプで排気した。その結果、容器内のポリアミド酸溶液は発泡して、円錐型の容器内に発泡体が得られた。
減圧状態（１Ｔｏｒｒ以下）の状態で真空オーブンを２１０℃まで昇温させて１時間真空中で焼成を行った。
内部の固形分を取り出して、１００℃から４２０℃まで１時間かけて焼成を行いポリイミド発泡体を得た。
このポリイミド発泡体の密度は６．２ｋｇ/ｍ^３であった。

The polyamic acid solution was placed in a conical container (a container having a diameter of 20 cm and a height of 20 cm) whose inner wall was coated with a fluororesin, and then placed in a vacuum drying apparatus. The temperature of the vacuum drying apparatus at the time of charging was charged at 100 ° C. The vacuum was exhausted at once with a vacuum pump so that the degree of vacuum was 1 Torr or less. As a result, the polyamic acid solution in the container foamed, and a foam was obtained in the conical container.
In a state of reduced pressure (1 Torr or less), the vacuum oven was heated to 210 ° C. and baked in vacuum for 1 hour.
The solid content inside was taken out and baked from 100 ° C. to 420 ° C. over 1 hour to obtain a polyimide foam.
The density of this polyimide foam was 6.2 kg / m ³ .

(Example 3)
In a 2 L glass separable flask, a siloxane diamine (manufactured by Dow Corning Toray: trade name BY16-853U, molecular weight 910, R ₁ and R ₂ in the general formula (1) are methyl groups, n = 3 M = 9), 36.4 g (0.04 mol) and 345 g of N, N-dimethylformamide were added and stirred. To this solution, 32.1 g (0.16 mol) of 4,4-diaminodiphenyl ether was added and dissolved by stirring. Next, 43.6 g (0.20 mol) of pyromellitic dianhydride was added to obtain a polyamic acid solution (solid content concentration 18%).

上記ポリアミド酸溶液をフッ素樹脂で内壁をコーティングした円錐型の容器（直径が２０ｃｍで高さが２０ｃｍの容器）に入れて、真空乾燥装置に投入した。投入時の真空乾燥装置の温度は１００℃で投入した。また、真空度は１Ｔｏｒｒ以下になるように、一気に真空ポンプで排気した。その結果、容器内のポリアミド酸溶液は発泡して、円錐型の容器内に発泡体が得られた。
減圧状態（１Ｔｏｒｒ以下）の状態で真空オーブンを２１０℃まで昇温させて１時間真空中で焼成を行った。
内部の固形分を取り出して、１００℃から４２０℃まで１時間かけて焼成を行いポリイミド発泡体を得た。
このポリイミド発泡体の密度は４.５ｋｇ/ｍ^３であった。

The polyamic acid solution was placed in a conical container (a container having a diameter of 20 cm and a height of 20 cm) whose inner wall was coated with a fluororesin, and then placed in a vacuum drying apparatus. The temperature of the vacuum drying apparatus at the time of charging was charged at 100 ° C. The vacuum was exhausted at once with a vacuum pump so that the degree of vacuum was 1 Torr or less. As a result, the polyamic acid solution in the container foamed, and a foam was obtained in the conical container.
In a state of reduced pressure (1 Torr or less), the vacuum oven was heated to 210 ° C. and baked in vacuum for 1 hour.
The solid content inside was taken out and baked from 100 ° C. to 420 ° C. over 1 hour to obtain a polyimide foam.
The density of this polyimide foam was 4.5 kg / m ³ .

Example 4
In a 2 L glass separable flask, a siloxane diamine (manufactured by Dow Corning Toray: trade name BY16-853U, molecular weight 910, R ₁ and R ₂ in the general formula (1) are methyl groups, n = 3 M = 9), 9.42 g (0.01 mol) and 281 g of N, N-dimethylformamide were added and stirred. To this solution, 18.0 g (0.09 mol) of 4,4-diaminodiphenyl ether and 10.8 g (0.10 mol) of p-phenylenediamine were added and dissolved by stirring. Next, 43.6 g (0.20 mol) of pyromellitic dianhydride was added to obtain a polyamic acid solution (solid content concentration 18%).

上記ポリアミド酸溶液をフッ素樹脂で内壁をコーティングした円錐型の容器（直径が２０ｃｍで高さが２０ｃｍの容器）に入れて、真空乾燥装置に投入した。投入時の真空乾燥装置の温度は１００℃で投入した。また、真空度は１Ｔｏｒｒ以下になるように、一気に真空ポンプで排気した。その結果、容器内のポリアミド酸溶液は発泡して、円錐型の容器内に発泡体が得られた。
減圧状態（１Ｔｏｒｒ以下）の状態で真空オーブンを２１０℃まで昇温させて１時間真空中で焼成を行った。
内部の固形分を取り出して、１００℃から４２０℃まで１時間かけて焼成を行いポリイミド発泡体を得た。
このポリイミド発泡体の密度は８．１ｋｇ/ｍ^３であった。

The polyamic acid solution was placed in a conical container (a container having a diameter of 20 cm and a height of 20 cm) whose inner wall was coated with a fluororesin, and then placed in a vacuum drying apparatus. The temperature of the vacuum drying apparatus at the time of charging was charged at 100 ° C. The vacuum was exhausted at once with a vacuum pump so that the degree of vacuum was 1 Torr or less. As a result, the polyamic acid solution in the container foamed, and a foam was obtained in the conical container.
In a state of reduced pressure (1 Torr or less), the vacuum oven was heated to 210 ° C. and baked in vacuum for 1 hour.
The solid content inside was taken out and baked from 100 ° C. to 420 ° C. over 1 hour to obtain a polyimide foam.
The density of this polyimide foam was 8.1 kg / m ³ .

(Comparative Example 1)
To a glass separable flask having a volume of 2 L, 381, g of N, N-dimethylformamide was added and stirred. To this solution, 40.1 g (0.20 mol) of 4,4-diaminodiphenyl ether was added and dissolved by stirring. Next, 43.6 g (0.20 mol) of pyromellitic dianhydride was added to obtain a polyamic acid solution (solid content concentration 18%).
The polyamic acid solution was placed in a conical container (a container having a diameter of 20 cm and a height of 20 cm) whose inner wall was coated with a fluororesin, and then placed in a vacuum drying apparatus. The temperature of the vacuum drying apparatus at the time of charging was charged at 100 ° C. The vacuum was exhausted at once with a vacuum pump so that the degree of vacuum was 1 Torr or less. However, this solution did not foam at all.

Claims (4)

  A polyimide foam comprising at least pyromellitic acid, diaminodiphenyl ether and siloxane diamine. Polyimide foam of claim 1, wherein the foam density of the polyimide foam is ^{1kg / m 3 ~10kg / m 3} .   The content rate of the siloxane diamine contained in the said polyimide foam is contained in the ratio of 0.5-30 mol with respect to 100 mol of all the diamines, The any one of Claims 1-2 characterized by the above-mentioned. Polyimide foam.   A method for producing a polyimide foam, comprising: forming a polyimide foam by decompressing and drying a polyamic acid solution comprising at least pyromellitic acid, diaminodiphenyl ether, and siloxane diamine.